Spin-labeled antitumor derivatives of podophyllotoxin

Three spin-labeled antitumor derivatives of podophyllotoxin, containing an iminoxyl radical, have been synthesized. Preliminary pharmacological tests showed that these derivatives have significant antitumor activity in several experimental tumor systems with a marked decrease in toxicity compared with the parent compound. The relative intensities of ESR signals of these spin-labeled compounds were linearly proportional to their concentrations, the levels of the agent in blood and organs of mice or rabbits can be measured via ESR spectrometry.